Guild dungeon points or GDP are acquired by running guild dungeons. Please read the thread entitled Guild Dungeon Runs to find out more information before you continued reading this post.
Lake in Dusk, Ruina Station, Epaulet of Dead: 1 point
Seal of Darkness: 2 points
Epaulet of Dead B2F, Forgotten Temple B1F: 3 points
Illusion Castle 1, Alter of Sienna B1F, Forbidden Island: 4 points
Illusion Castle 2, Alter of Sienna B2F: 5 points
Forgotten Temple B2F: 6 points
Maquina's Outpost: 7 points
CA 1-3: 2 points
CA 4/5: 3 points
To check the number of points you have please check the thread GDP Chart.